Radiating apparatus and method



06k. 14, 1941. R, F. JAMES 2,258,765

RADIATING APPARATUS AND METHOD Filed July ll, 1934 2 Sheets-Sheet l ro maw-Poing? ATTORNEY Oct. 14, 1941. R. F. JAMES 2,258,765

RADIATING APPARATUS AND METHOD Filed July 1l, 1954 2 sheets-sheet 2 1| nmlumuu l] Mmmm-r 16/{ l if suol Patented Oct. 14, 1941 it; mr

ur carica and Manufacturing Company, East Pittsburgh, Pa., a corporation ci Pennsylvania Application July 11', 1934, Serial No. 734,620

14 Claims.

My invention relates to sources of electromagnetic radiations and particularly to such 4sources for the generation of ultra-violet radiations having a desired bactericidal effect without producing detrimental reaction, and constitutes a continuation in part of my copending application Serial No. 532,655, led April 24, 1931.

It has long been recognized in the prior art that ultra-violet light has a decided bactericidal andtherapeutic elect. However, the operation of prior art devices has been inherently accom? panied by the generation of considerable heat as well as by the emission vof the short wave u lengths of ultra-violet which cause ionization of the surrounding atmosphere forming ozonerthus producing, in many instances, a deleterious eiect on irradiated material. Moreover, it has been recognized that the generation of ultra-violet light radiations of certain intensities having a high bactericidal effect are accompanied by the generation of radiations which tend to injure or destroy portions of the host or material being irradiated.

For example, in the irradiation of food products, such as meat andthe like, certain wave lengths are required to prevent bacteria and ftmgous growth. However, in the irradiation of these food products radiations of detrimental character are also generated causing chemical reactions either directly by the radiations or by oxidation due to' the prevalence of ozone, to portions of the material which it is not desired to treat, thus requiring filtering of these radiations of undesirable quality and allowing only the radiations of bactericidal wave lengths to irradiate the food products. Y

While the utilization of auxiliary filters prevents undesired radiations from actually irradiating the material by direct radiation, it does not preclude these radiations from indirectly alecting the palatability of the material. Particularly is this noticeable in conned spaces, where ozone is very prevalent due to the action of these undesired radiations upon the surrounding atmosphere which inherently causes a chemical reaction in the material.

It has also beenA proposed in the'prior art to construct an .ultra violet lamp operable at a temperature of C. by limiting the vapor presate the lamp at a low current density. In such .a device, however, the cathode is dependent upon thermionic emission for operation and is accordingly heated, either from an auxiliary source or maximum proportion of eii'ective bactericidal and' by the heat generated by the discharge, thus limiting the minimum operating temperature ol the device to 50 C. Inasmuch as this minimum temperature is comparatively high the device is impracticalfor use in a domestic refrigerator or other places where considerable heat is objectionable, because it would so aiect the temperature thereof as to cause the refrigerating apparatus to run substantially continuously to obtain desired low refrigerating temperatures. Moreover, no consideration has been given in such a structure to the elimination vof the inherent formation of ozone which would, as before stated, ailect the material being irradiated.

It is equally possible to operate a tube-between cold electrodes in such a manner that the tube wall be kept at a low temperature for the purpose of producing .the ultra-violet radiation at wave lengths 0f v2530 t0 2540 A. U.

This can be eectively accomplished by utilizing a large tube wall surface to produce eiective cooling by the surrounding air, but this necessarily requires such a large envelope as to extremely limit the eld of application of the tube rendering it particularly unsuited in confined spaces, suchas refrigerators and the like. Also in both these cases no attention is given tothe production of the maximum effective radiation with a minimum production of heat.

By my present invention I obviate these objectionable featuresinherent in prior art structures by the construction of an ultra-violetlight generator wherein the-character of the emitted radiations is more or less limited to only those wave lengths having a highly bactericidal eil'ect while radiations of wave lengths which are detrimental are eliminated, thus dispensingl with the necessity for auxiliary iilters. -Moreover, by the utilization of cold electrodes between which a discharge occurs independent of thermionic emission, by ionization 'of a gaseous medium by the voltage gradient applied to the electrodes, there results Ia generation of radiations substantially limited to a deiinite spectral range,` accompanied by an inappreciable generation of heat from the discharge.

A still further vcharacteristic of my present invention resides in the fact that I limit the bulk of the emitted radiations in the highly bactericidal region to a band which is more than substantially 40% of the total radiations generated. Over of the radiations within this definite spectral range are generated in a narrow band at approximately 2537 ,A, U.,thus obtaining a fungicidal radiations with a minimum generation of heat and with a minimum of radiations of detrimental wave lengths.

One of the principal objects of my present invention is the provision of what might be termed a cold source of ultra-violet light, in that radiations having desired bactericidal characteristics without attendant detrimental effects, are produced with a minimum generation of heat, the device being operable at substantially the temperature of the surrounding or ambient medium in which it is placed. Y

Another object of my invention is the provision of an ultra-violet light generator having exceptional bactericidal and fungicidal qualities for the irradiation of food products and which causes no detrimental eifects tending to alter the palatability of the irradiated material.

A further object of the invention is the provision of an ultra-violet light generator i'or producing radiations of a desired wave length suitable for irradiation and therapeutic purposes wherein the intensity of the radiations is so lim- Fig. 6 is an elevational view of a domestic refrigerator showing one application of the various f usages of my present invention,

itedas to produce only a desired bactericidal or therapeutic eiIect without any appreciable ionization or chemical reaction to thel irradiated material, or generation of heat during operation.

A still further object of my invention is the provision of an ultra-violet light generator of bactericidal radiations, without accompanying detrimental radiations thus dispensing with the necessity for auxiliary filters."

An additional object of my invention is the provision of an ultra-violet light generator for producing radiations limited to bactericidal wave lengths, wherein discharge during operation of the generator is unaccompanied by the generation of appreciable heat, by the utilization of solid electrodes together with a proper gas mixture, with the character of the discharge solely dependent upon ionization of the-mixture.

Another object of my invention is the provision of an ultra-violet light generator for producing bactericidal radiations without -detrimental action onto irradiated material and capablo of operation at the temperature of the ambient medium, thus rendering the device applicable to domestic refrigerators for the irradiation of stored food products with a minimum eect upon the refrigerating temperature.

A further object of my present invention is the provision of a therapeutic device capable of generating ultra-violet light radiations which will not deleteriously aifect human tissue, and emitting only benecial radiations unaccompanied by the generation of appreciable heat, so that it may be actually inserted in tissues and cavities of the" human body without discomfort to a patient.

Still further objects of my present invention will become apparent to those skilled in the art by reference to the accompanying drawings wherein:

Figure 1 is an elevational view, partly in section, of an ultra-violetfliglii-l generator constructed in accordance with my present invention,

Fig. 2 is an elevational view showing a modiilcation of my ultra-violet light generator illustrated in Fig. 1, .i

Fig. 3 is a longitudinal sectional view of a vaginal applicator embodying the features oi' my present invention,

Fig. 4 is a sectional view taken at right anglesto that of Fig. 3,

Fig. 5 is a cross sectional view taken on the line V--V of Fig. 4,

Fig. '1 is a graphic illustration of the distribution of energy emitted by my ultra-violet light generator, and

Fig. 8 is a composite graphic illustration of the relationship of current, voltage, and temperature during operation of my ultra-violet light generator.

In its broadest aspects, my invention comprises an evacuated envelope formed of a material pervious to ultra-violet radiations within a preselected portion of the spectrum, an ionizable medium within the envelope, and means for impressing` a voltage on the medium sufilcient to cause ionization thereof with attendant generation of electro-magnetic radiations within the ultra-violet region of the spectrum. While various gases such as argon, neon, helium, krypton and xenon, and combinations thereof may be used to obtain ultra-violet radiations, I have found it Apreferable to utilize an ionizable medium composed of 60% neon and 40% argon together with a small quantity of mercury, for reasons hereinafter more specifically noted.

By regulating the gas or mixture of gases, the pressures thereof, the applied potential and the material of the container, it is possible to obtain bands of radiations that have a preponderance in the ultra-violet. I have found that by proper conditions of pressure of the ionizable medium, the potential applied to the ionizable medium, and the selection of the gas mixture, the amount of energy consumed in the discharge for the production of a given amount of radiations may be maintained at a minimum, thereby tending to decrease the amount of heat generated during `operation of the tube. Ionization of the gaseous ,and 4000 A. U. or longer is desired. However,

as such a range of the spectral region is accompanied by the generation of detrimental radiations as well as bactericidal radiations, I prefer to utilize an envelope composed of boro-silicate glass free from iron having an ultra-violet transparency for wave lengths longer than 2500 A. U., such as a glass `commercially known as Corex D, or Corning 972, High Transmission Ultra-violet Glass, which is a' form of Corex glass, in which range lies the most highly bactericidal radiations.

Electrodes I and 1 are disposed `within the envelope at each end thereof andsupported by suitable leading-in conductors 8 and 9, 4such as tungsten wire or the like, which are sealed into the envelope and project outside the tube. These electrodes may be of tubular or any other de- 'sired Aconiiguration constructed of a good conducting material, preferably of a metal, such as iron, aluminum, or nickel, which will not discharge minute metal particles or a metallic va- Apor into the gas, and the `envelope may be of a shape conforming to the` speciiic application. In Fig. 2 I have shown a modiilcation of the structure illustrated in Fig. 1, differing only in that supplemental electrodes I0 and I2 are employed tity of mercury in order to increase the intensity of the ultra-violet radiation, the pressure of the medium being about 8 millimeters.

'I'his quantity of mercury added to the admix- 10 ture is small, so that during operation of the device the mercury in the enective path of the generated radiations will be lsubstantially completely vaporized, and particles of excess will notr act as a screen absorbing ultra-violet radiations. V

By applying a potential to the electrodes 6 and 1 from a suitable Source of alternating current, such as a transformer or the like (not shown), ionization of the gaseous medium occurs due to the voltage "gradient, thus causing a positive column discharge between the electrodes.

Preferably the transformer is of the current limiting type whereby a potential of suilicient magnitude, or about 2000 volts, is yavailable for starting the discharge, but during operation the voltage drop across the tube is only about 500 volts and the current approximately 25 milliamperes as shown in Fig. 8. 'Due to the selection of the gases which carry the discharge current and since the electrodes are cold, being independent f thermionic emission by heating either from an extrinsic source or by the discharge it-v self, ionization of the medium being caused by the voltage gradient, the resulting discharge and generation of ultra-violet radiations is independent of thermionic emission and thus substantially unaccompanied by the generation of heat. The quantity of mercury, as before noted, being small does not act as a screen for the generated ultra-violet radiations and in addition contributes to the generation of maximum effective bactericidal' radiations with inappreciable heat.

Moreover,` as before noted, the composition approximate 100 F. As the ambient temperature 'is assumed to be 75F. it is thus obvious that at this voltage and current the temperature of operation of the tube is 25 F. above ambient. However, a decrease of current and voltage causes a decrease in the operating temperature of the tube bringing it nearer to that of the ambient medium in whicirtheitube is placed. By the same token. either an increase in current and voltage, or a decrease inthe electrode spacing, as when a device, suchfas shown in Fig. 2, is employed, causes the lamp to operate 4at a higher temperature, as the electrode drop is xed and relatively large. When the lamp is operated in a refrigerator, it or the distance between electrodes had best be short, so that its length or the distance between electrodes may be less than three inches, as indicated in Fig. 2. The reason forv this is that the ultra-violet output of the lamp is greater at temperatures above those in a normal refrigerator. Of course, the lamp should not be operated so hot that a substantial amount of visible ,light is emitted by the electrodes. I

Spectographic analysis including studies of energy distribution curves shows a definite required relationship between the envelope material and cross sectional diameter, the particular -gases and pressure. together with the applied potential and the current which is susceptible to mathematical expression in order to produce the results I obtain. Such analysis also shows that inasmuch as the quantity of mercury is small, as before stated, the energy distribution in the bactericidal active portion of the ultra-violet 'region generated :by my tube, namely, that portion lying between 2500 A. U. and 3100 A. U. is such, that mercury radiations are produced in a very narrow band within this region between 2530 A. U. and 2540 A.U. which are more than of the total radiations generated between 2500 A. U. and 3100 A. U.

This is shown more clearly in Fig. '7 wherein I have graphically illustrated the energy distribution generated and emitted by ione form of my of the envelope is such that over 90% of the 45 tube constructed of glass' having certain transradiations in the detrimental region, namely, of wave-lengths below 2500 A. U. are suppressed or absorbed while substantially all beneficial bactericidal radiations are transmitted, the envelope mission characteristics, as .actually shown by a spectral microphotometer with the abscissas representing wave lengths and the ordinate representing arbitrary units of intensity. The total may be of minimum size, as a large surface area is 50 energy distribution generated by my tube of not required to dissipate heat, as the discharge itself is unaccompanied by a substantialgeneration of the latter.

Under actual conditions of operation with a an internal diameter of 1.27 centimeters, and a wall thickness of l millimeter, 'together with the aforenoted gaseous me'dium at a pressure of 8 mm. a current of less than 25 milliamperes is By reference to Fig. 8 a compositegraphic illus- 65 tra-tion is shown wherein the upper portion represents the temperature range of operation of my tube for different voltage and current ranges and in the lower portion of this figure, with the abscissas indicating current and the ordinates voltage, the current-voltage curve is shown. From this illustration it is readily manifest that with a voltage drop across the tube of 500 volts a current of approxim-ately 25 milliamperes will flow and the temperature of operation of the tube will passedand the voltage drop across thev tube is 60 various wave lengths is represented by the lightly shaded portion A and the darker portion B. From an analysis of this figure it is obvious that more than 60% ofthe generatedradiations betube'having an overall length of 46 centimeters, 55 tween 2500 A. U. and about 3100 A. U. are confined to a narrow band between 2530 A. U. and 2540 A. U. with the remaining less than 40% being distributed throughout the remainder of the specied spectral range.

The particular envelope of the tube represented has transmission characteristics as illustrated by the heavy dotted line so that the actual emitted radiations lying between 2500 A. U. and about 3100 A. U. are such, that somewhat less than substantially 40% of the total energy .given oi in this region is produced by the well known and relatively veryintense mercury lines in the band between 2530 A. U. and 2540 A. U. So by the darkly shaded portion of Fig. 7, indicates somewhat less than substantially 40% of the total radiations emitted between 2500 A. U. and about 3100 A. U. are restricted to the narrow band between 2530 A. U. and 2540 A. U. and the remaining 60% of the emitted radiations distributed throughout the remainder of the emitted spectral range.v If an envelope having better transmission characteristics is employed, a much greater -proportion of the generated bactericidal radiations will be transmitted.

Accordingly the mercury radiations generated by my tube, and particularly those from `the mercury lines below 2500 A. U. are effectively eliminated, while those between 2530 and 2540 A. U. are not so reduced to such an intensity as to obviate satisfactory bactericidal and fungicidal action. Due to this limitation of the intensity, not only is a highly beneficial bactericidal action obtained without detrimental chemical reaction to the surrounding media and particularly the material irradiated, but because of the operation of the device being unaccompanied by the generation of an appreciable amount of heat, the tube will operate at a temperature as low as 5 to 10C.

This feature renders my tube particularly adaptable for the irradiation of food products stored in domestic refrigerators in that operation of the tube has an inappreciable eifect upon the refrigerating temperatures. Moreover, upon failure of the refrigerating apparatus for any particularl reason, with an attendant rise in temperature of the refrigerator to room temperature, there would ordinarily follow an increase in the propagation of bacteria and fungous growths which is avoided by the use of my lamp.

A still further characteristic of my tube is that, starting at a low temperature, upon an increase in temperature of the ambient medium there follows an increase in the operating temperature of the tube which is always slightly above that of the ambient medium. This likewise causes a resulting increase in the intensity of the emitted radiations due to increase in mercury pressure, thereby counteracting what would be,a normal activation of these growths upon increases in temperature within a refrigerator.

Referring now more specifically to Fig. 6 I have shown my novel ultra-violet generator adapted to a domestic refrigerator comprising a container I5 provided with any suitable type of refrigerating apparatus shown generally at I6. A tube I1, such as shown in Fig. 1 or Fig. 2, is preferably placed near the top of the refrigerator so that short wave radiations therefrom will be directed on the food disposed on the shelves I8. The food may be irradiated for long periods of time without danger of affecting the palatability thereof as would result with tubes of higher intensities and more particularly with still shorter wave length radiations.

The advantageous features previously mentioned which are obtainable with my ultra-violet light generator renders it applicable to a wider scope of medical or surgical physiotherapy or heliotherapy. In instances of surgical sepsis, the source may be buried in the wound and left for relatively long periods of time without the danger of breaking `down the tissue, causing erythema or discomfort to a patient due to attendant generation of heat as in prior art devices.

In Figs. 3 and 4 I have illustrated a vaginal applicator constructed in accordance with my present invention. which renders it highly erlicient for sterilization and other hygienic purposes. The envelope 5a in this modification is bent upon itself to form a return as shown in Fig. 5, with opposite ends of the tube adjacent each other and supported within a dielectric case 22. The

ends of the tube areenlarged, as shown at Il and 24, for receiving the electrodes 'ta and 1a. When the tube'is energized the discharge longitudinally along the envelope and back forming substantially a U-shaped path and. as the envelope is pervious to ultra-violet light of predetermined wave lengths and the intensity is such that no detrimental effects are produced.

the device may 'be-inserted without danger of burning or otherwise harming'the mucous lining of the vagina or uterus thereby advantageously treating infections of various kinds.

Moreover, experiments with my ultra-violet light generator have shown that it can very advantageously be utilized for increasing the vitamin D content of various food stuffs, such as milk, vegetable oil, butter. etc., without affecting the temperature thereof or causing chemical changes tending to render the irradiated food unpalatable. Also algae'and other impurities found in water may be killed and the water rendered completely sterile without changing its chemical content.

It thus becomes obvious to those skilled in the art that I have provided'an electro-magnetic radiation generator for producing ultra-violet light within a predetermined region of the spectrum and the intensity thereof is so limited that only desired bactericidal results are obtained without detrimental chemical or other reactions occurring. Inasmuch `as the generation of the radiations are accompanied by an inappreciable generation of heat, the tube may be utilized in a domestic refrigerator without danger of aecting the refrigerating temperature thereof. Moreover, the device is readily applicable to physiotherapy, and heliotherapy in that it may be brought into direct contact with the body of a patient without fear of burning the tissues or causing erythema.

Having thus described several embodiments of my invention I do not desire to be limited thereto. as various other modifications of the same may be made without departing from the spirit and scope of the appended claims.

What is claimed:

l. The method of operating an electric discharge device for producing ultra-violet rays for sterilization purposes, comprising a Corex envelope which is transparent to wave-lengths above 2500 Angstrom units and opaque to those below 2500 Angstrom units, a pair oi.' nonthermionic solid electrodes sealed through said envelope, and a rare gaseous filling at a pressure of 8 mrn. of mercury together with a filling of mercury vapor contained within said envelope. which comprises impressing a potential across the electrodes and adjusting the current density to a value less than 25 milliamperes per square centimeter.

2. An ultra-violet light generator comprising a tubular envelope transparent to light above about 2500 A. U., but absorbent to nearly all radiations below that wave length, containing a pair of non-thermione solid main electrodes disposed one at each end, said envelope also containing a rare gaseous filling, admixed with mercury vapor, at a low pressure, and said generator being operable at low current densities to produce a discharge having a large proportion of its radiations between 2500 and 2800 A. U., so as to be particularly effective for bactericidal and fungicidal purposes, while weak for producing aste an'd odor changes in food irradiated there- 2,258,765` s. 'rne method of treating feeavto destroy bacteria which comprisesl initiating an ebectrical discharge in an atmosphere of mercury vapor and at least one inert gas contained in an envelope 4of Corex` glass which transmits wavelengths above, 2500 Angstrom units but which absorbs those below 2500 Angstrom units, adjusting the current density across the bore of the discharge envelope to cause the radiationemitted by the discharge to have, of its ultra-violet radiation below 3130 Angstrom units, a large proportion between 2500 and 2800 Angstrom units, and exposing the food to said radiation fora time suflicient to produce substantially complete s urface sterilization of thel food,but not suicient to produce harmful eiects on the food.

4. The method of claim 3, inwhich the food is exposed for a time suilicient to produce substantially complete surface sterilization, but not suicient to produce`tastechange. l

5. An ultra-violet radiation generator comprising an envelope having a generally cylindrical intermediate portion transparent to raes te be pemeunrly exreeuve for beuerieiaei and fungicidal purposes and sumciently free from taste-changing and Aother harmful radiations,

an ionizable medium comprising a rare gaseous diations of wave lengths above about 2500 A. U.,

but absorbent to nearly all radiations below said wave length, a pair of electrodes disposed one adjacent each-end of, and an ionizable medium comprising a rare gaseous lling admixed with mercury vapor at low pressure, sealed in, said envelope, said generator being operable at low current densities to produce a discharge having a large proportion of its radiations between 2500 and 2800 A. U., so as to be particularly effective for bactericidal and fungicidal purposes, while Weak for producing taste and odor changes in food irradiated thereby.

thereby producing an ultra-violet radiation- 6. The method of operating an electric dis- A charge device to produce ultra-violet rays for sterilization purposes, said device comprising an envelope with an intermediate portion generally cylindrical and transparent to radiations having wave lengths longer than 2500 A. U., but absorbent to nearly all radiations having wave lengths shorter than 2500 A. U., a pair of electrodes sealed into said envelope and disposed one adjacent each end thereof, a rare gaseous filling admixed with mercury vapor and at a low pressure enclosed in said envelope, comprising impressing a potential across said electrodes and adjusting the resulting current so that its density across said intermediate portion is less than forty milliamperes per square centimeter, to minimize the .generation of detrimental radiations, and thereby producing an electrical discharge having a large proportion of its radiations between 2500 and 2800 A. U., and a minimum proportion detrimental -to food, whereby said radiations are particularly effective for bactericidal and fungicidal purposes, while weak for producing taste and odor changes infood irradiated thereby. i'

7. The method of treating `a host, comprising producing'an electrical discharge, which generates ultra-violet radiations, between spaced electrodes in a glass envelope containing a rare gaseous filling admixed with mercury vapor at low pressure, keeping the current density of said discharge low, and using glass, transparent to radiations' having wave lengths longer than 2500 A. U., butabsorbent to nearly all radiations having wave lengths shorter than 2500 A. U., for the envelope, so that the radiations which are emitted from said envelope will have a large proportion between 2500 and 2800 A. U., and a minimum proportion detrimental to said host, so

that substantially complete surface sterilization 'can be obtained before a harmful eilect occurs,

and subjecting said host to said radiations of an intensify and rer the limited perid of time neeessary to eii'ect such sterilization withoutetrlmentally changing said host.

8. An ultra-violet radiation generator comprising an envelope having an intermediate portion ,transparent to radiations of wave lengths above about 2500 A. U., but absorbent to nearly all ra` diations below said wave length, a pair of electrodes disposed one adjacent each end of,-and

filling admixed with mercury vapor at low pressure, sealed in, said envelope, said generator bing operable at low current Vdensities to produce a discharge -having but a small proportion of its radiations outside .of the range between 2500 and 2800 A. U., so'as to be weak for producing taste and odor changes in food irradiated thereby.

9. The method of operating a discharge device to produce ultra-violet rays for sterilization purposes, comprising controlling the source of energy to said device, to minimize the generation of detrimental radiations, by adjusting the resulting current so that its density is less than forty milliamperes per square centimeter, and

.generating electrical discharge providing radia- -tions having a large proportion between 2500 and ,2800 A. U., and a minimum proportion detrimental to food, causing the generated radiations to pass through the wall of the discharge device envelope consisting of glass which absorbs undesired radiations, whereby the emitted radiations are particularly effective for bactericidal and fungicidal purposes, while weak for produc- .ing taste and odor changes yin food irradiated thereby.

10. The method of treating a host, comprising producing an electrical discharge, which generates ultra-violet radiations, between spaced electrodes in 'a glass envelope containing a rare gaseous filling admixedwith mercury vapor at low pressure, keeping the current density. of said discharge low, and using such glass for the envelope, that undesired harmful radiations generated by the discharge are absorbed, so that the radiations which are emitted will be particularly e'ective for bactericidal and fungicidal purposes and suiliciently free from taste changing and other harmful radiations, that substantially complete surface sterilization can be obtained before a harmful eiect occurs, and subjecting said host'to said radiations 'of an intensity and for the limited period of time necessary to eiect such sterilization without detrimentally changing said host.

111. An electric discharge lamp for treatment of air borne or surface organisms, said lamp comprising a sealed elongated tubular envelope of Corex glass of a thickness such that radiations of wavelengths greater than 2500 A. U. are transmitted by the glass, but the ozoneproducing radiations below 2500 A. U. are substantially absorbed to prevent the formation of an objectionable amount of ozone in the path of the radiation from the lamp, electrodes at sure such as to cause the mercury vapor to produce its most intense ultra-violet radiation in the neighborhood of 2500A. U. at low current density, and apparatus for operating the lamp at such current density.

12. An electric discharge lamp comprising a sealed vtubular envelope of Corex glass, electrodes at opposite ends o! said envelope. anda miitture of mercury vapor and a rare gas at low Y 10 whereby the remainder is particularly effective pressure within said envelope,` and apparatus for operating said lamp at a low current density: said mixture having a pressure such .as to 4emit at such current density its most intense ultraviolet radiations in the neighborhood of 2500 f 5 trical discharge having a large` proportion of its` radiationsbetweenBBOO and 2800 A. U.. and a minimum proportion `detrimental to food. causing the generated radiations yto pass through glass which absorbs undesired portions thereof,

'for bactericidal and fungicidal, purposes, while weak for producing taste and odor changes in g food irradiated thereby. i

14. The method of treating a host comprising A. U. in wave length, andthe envelope being of a 15 producing radiations between 2500` md 2300 thickness greatenough to absorb4 substantially all radiations below 2500 A. U. in wave length. to prevent the formation of appreciable ozone in the path of radiation from the lamp, but not great enough to substantially absorb radiations above 2500 A. U., whereby the entire combination formsa unitsuitable for irradiating. without damaging food. y

13. The method of operating an electric discharge device to produce ultra-violet rays for sterilization purposes, comprising impressing a potential across the electrodes of, and adjust- Angstrom units admixed with a negligible proportion detrimental'to said host, so as to be parlticuiarly effective for bactericidal and fungicidal purposes and sumciently free from taste chang- `20 ing and other4 harmful radiations that substantially complete surface sterilization lcan be obtained before a harmfuieifect occurs. and subjecting said host to said radiations of an intensity and for a period of time necessary toeifect such 25 sterilization without detrimentally changing said host.

y ROBERT F. JAMES. 

